Recently, in order to improve the safety of vehicle occupants, many systems have been proposed. Those systems include, for example, a system for determining whether an occupant seated on a seat is an adult based on the weight of the occupant, and a system that enables the actuation of an air bag or the retention of a seat belt to be satisfactorily performed based on the weight of the occupant seated on the seat.
For example, a system disclosed in the below-mentioned patent document 1 has weight detecting sensors respectively provided at four supporting leg portions that support a vehicle seat, an electronic control unit which includes a determining circuit that determines whether or not an occupant is an adult based on the signals from the weight detecting sensors, and an air bag electronic control unit which is connected to the electronic control unit. The weight detecting sensors and the electronic control unit are connected by a wire harness which is configured by a predetermined number of electric wires. Since four weight detecting sensors are provided for each seat, many wire harnesses (electric wires) are connected to the electronic control unit.